Section 8 bedroom height requirement.

[Jerald Sander]

I'm converting attic space to two bedrooms (hopefully) in north St. Louis County, and want to make sure I understand the ceiling height requirement for sloped ceilings.  Am seeing different information depending on where I look:  7' over 75% of the space that's at least 5' high; 6'8" over 50%; and other combinations.  If I go Section 8 (haven't decided yet), is there one set of Federal rules and does anyone know what they are?  Or can local offices set their own rules?  If not Section 8, do St. Louis County rules apply?  I'm getting the feeling some jurisdictions avoid putting rules in writing to allow latitude, and you just have to have an inspection and roll the dice.  Anyone have experience with this?  Thanks in advance.